Analysis On Bearing Characteristics Of Karst Cave Roof Under Highway Bridge Pile Foundation

With the continuous extension of my country’s road network,bridges,as an important part of the road,are inevitably built in karst areas.The geological conditions of the karst area are complex,and many hidden caves were not discovered in the initial geological exploration stage,but were discovered as the project progressed,or because the route pattern could not bypass the caves,some bridge pile foundations were buried under the caves.When the roof bearing capacity of karst cave can not meet the requirements,the pile foundation of the bridge will be unstable and the bridge cannot be used normally.Therefore,it’s important to analyze the bearing characteristics of karst cave roof under bridge pile foundation.Based on the Mutong Temple Interchange Project in Shanxi Province,this paper uses on-site surveys,theoretical analysis,indoor model tests,and numerical simulations to analyze the bearing properties of the cavern underneath the bridge pile foundation.The main research contents are as follows:（1）On the basis of drilling,the high-density electrical method and transient Rayleigh wave method are used to conduct in-depth and detailed surveys of the engineering area.Obtain the development and distribution characteristics of karst.The survey results are compared and analyzed,and the spatial location model of pile foundation and karst cave are established.（2）The methods for evaluating the stability of cave roofs in karst areas are summarized,and the calculation formula for ultimate bearing capacity of cave roofs is derived based on the Hoek-Brown strength criterion.The indoor model test is used to study the stress and deformation characteristics of the pile foundation and the cave roof under actual engineering conditions,analyze the stability and bearing characteristics of the cave roof,and compare the theoretical analysis results with the indoor model test results.（3）Use FLAC^3D to simulate bridge pile foundations,analyze the load and displacement law of bridge pile foundation and roof,study the distribution characteristics of the roof plastic zone.The reliability of the numerical simulation technology is verified through a comparative analysis with the results obtained from the indoor model test.To study the bearing capacity of the roof of the karst cave beneath the pile foundation of the bridge under different factors（the GSI parameters of the roof,the thickness of the roof,the horizontal distance between the cave and the pile,and the diameter of the cave）.The research results are helpful for the investigation of karst and the design of bridge pile foundation.